1. Field of the Invention
In a general sense, the invention is directed to systems and methods for treating interior tissue regions of the body. More specifically, the invention is directed to systems and methods for treating dysfunction in body sphincters and adjoining tissue, e.g., in and around the lower esophageal sphincter and cardia of the stomach.
2. Description of the Background Art
The gastrointestinal (GI) tract extends from the mouth to the anus, and includes the esophagus, stomach, small and large intestines, and rectum. Along the way, ring-like muscle fibers called sphincters control the passage of food from one specialized portion of the GI tract to another. The GI tract is lined with a mucosal layer about 1-2 mm thick that absorbs and secretes substances involved in the digestion of food and protects the body's own tissue from self-digestion. The esophagus is a muscular tube that extends from the pharynx through the esophageal hiatus of the diaphragm to the stomach. Peristalsis of the esophagus propels food toward the stomach as well as clears any refluxed contents of the stomach.
The junction of the esophagus with the stomach is controlled by the lower esophageal sphincter (LES), a thickened circular ring of smooth esophageal muscle. The LES straddles the squamocolumnar junction, or z-line--a transition in esophageal tissue structure that can be identified endoscopically. At rest, the LES maintains a high-pressure zone between 10 and 30 mm Hg above intragastric pressures. The LES relaxes before the esophagus contracts, and allows food to pass through to the stomach. After food passes into the stomach, the LES constricts to prevent the contents from regurgitating into the esophagus. The resting tone of the LES is maintained by muscular and nerve mechanisms, as well as different reflex mechanisms, physiologic alterations, and ingested substances. Transient LES relaxations may manifest independently of swallowing. This relaxation is often associated with transient gastroesophageal reflux in normal people. Muscular contractions of the diaphragm around the esophageal hiatus during breathing serve as a diaphragmatic sphincter that offers secondary augmentation of lower esophageal sphincter pressure to prevent reflux.
The stomach stores, dissolves, and partially digests the contents of a meal, then delivers this partially digested food across the pyloric sphincter into the duodenum of the small intestine in amounts optimal for maximal digestion and absorption. Feelings of satiety are influenced by the vagally modulated muscle tone of the stomach and duodenum as well as through the reception and production of biochemicals (e.g., hormones) therein, particularly the gastric antrum.
Finally, after passage of undigested food into the large intestine, it is passed out of the body through the anal sphincter. Fluids unused by the body are passed from the kidneys into the bladder, where a urinary sphincter controls their release.
A variety of diseases and ailments arise from the dysfunction of a sphincter. Dysfunction of the lower esophageal sphincter, typically manifest through transient, relaxations, leads to reflux of stomach acids into the esophagus. One of the primary causes of the sphincter relaxations is believed to be aberrant vagally-mediated nerve impulses to the LES and cardia (upper part of the stomach). This condition, called Gastroesophageal Reflux Disease (GERD), creates discomfort such as heartburn and with time can begin to erode the lining of the esophagus—a condition that can progress to esophagitis and a pre-cancerous condition known as Barrett's Epithelium. Complications of the disease can progress to difficulty and pain in swallowing, stricture, perforation and bleeding, anemia, and weight loss. Dysfunction of the diaphragmatic sphincter, such as that caused by a hiatal hernia, can compound the problem of LES relaxations. It has been estimated that approximately 7% of the adult population suffers from GERD on a daily basis. The incidence of GERD increases markedly after the age of 40, and it is not uncommon for patients experiencing symptoms to wait years before seeking medical treatment.
Treatment of GERD includes drug therapy to reduce or block stomach acid secretions, and/or increase LES pressure and peristaltic motility of the esophagus. Most patients respond to drug therapy, but it is palliative in that it does not cure the underlying cause of sphincter dysfunction, and thus requires lifelong dependence. Invasive abdominal surgical intervention has been shown to be successful in improving sphincter competence. One procedure, called Nissen fundoplication, entails invasive, open abdominal surgery. The surgeon wraps the gastric fundis about the lower esophagus, to, in effect, create a new “valve.” Less invasive laparoscopic techniques have also been successful in emulating the Nissen fundoplication. As with other highly invasive procedures, antireflux surgery is associated with the risk of complications such as bleeding and perforation. In addition, a significant proportion of individuals undergoing laparascopic fundoplication report difficulty swallowing (dysphagia), inability to vomit or belch, and abdominal distention.
In response to the surgical risks and drug dependency of patients with GERD, new trans-oral endoscopic technologies are being evaluated to improve or cure the disease. One approach is the endoscopic creation and suturing of folds, or plications, in the esophageal or gastric tissue in proximity to the LES, as described by Swain, et al, [Abstract], Gastrointestinal Endoscopy, 1994; 40:AB35. Another approach, as described in U.S. Pat. No. 6,238,335, is the delivery of biopolymer bulking agents into the muscle wall of the esophagus. U.S. Pat. No. 6,112,123 describes RF energy delivery to the esophageal wall via a conductive medium. Also, as described in U.S. Pat. No. 6,056,744, RF energy has been delivered to the esophageal wall via discrete penetrating needles. The result is shrinkage of the tissue and interruption of vagal afferent pathways some believe to play a role in the transient relaxations of the LES.
The above endoscopic techniques all require the penetration of the esophageal wall with a needle-like device, which entails the additional risks of perforation or bleeding at the puncture sites. Special care and training by the physician is required to avoid patient injury. Use of the plication technique requires many operational steps and over time sutures have been reported to come loose and/or the tissue folds have diminished or disappeared. Control of the amount and location of bulking agent delivery remains an art form, and in some cases the agent has migrated from its original location. RF delivery with needles requires careful monitoring of impedance and temperature in the tissue to prevent coagulation around the needle and associated rapid increases in temperature. Lesion size is also limited by the needle size. Limitations of the design require additional steps of rotating the device to achieve additional lesions. Physicians have to be careful not to move the device during each of the multiple one-minute energy deliveries to ensure the needles do not tear the tissue.
Dysfunction of the anal sphincter leads to fecal incontinence, the loss of voluntary control of the sphincter to retain stool in the rectum. Fecal incontinence is frequently a result of childbearing injuries or prior anorectal surgery. In most patients, fecal incontinence is initially treated with conservative measures, such as biofeedback training, alteration of the stool consistency, and the use of colonic enemas or suppositories. Biofeedback is successful in approximately two-thirds of patients who retain some degree of rectal sensation and functioning of the external anal sphincter. However, multiple sessions are often necessary, and patients need to be highly motivated. Electronic home biofeedback systems are available and may be helpful as adjuvant therapy. Several surgical approaches to fecal incontinence have been tried, with varying success, when conservative management has failed. These treatments include sphincter repair, gracilis or gluteus muscle transposition to reconstruct an artificial sphincter, and sacral nerve root stimulation. The approach that is used depends on the cause of the incontinence and the expertise of the surgeon. Surgical interventions suffer from the same disadvantages discussed above with respect to GERD. An RF needle ablation device, similar in design to that described above for treatment of GERD, has been described in WO/01/80723. Potential device complications and use limitations are similar to those described for GERD.
Dysfunction of the urinary sphincter leads to urinary incontinence, the loss of voluntary control of the sphincter to retain urine in the bladder. In women this is usually manifest as stress urinary incontinence, where urine is leaked during coughing, sneezing, laughing, or exercising. It occurs when muscles and tissues in the pelvic floor are stretched and weakened during normal life events such as childbirth, chronic straining, obesity, and menopause. In men, urinary incontinence is usually a result of pressure of an enlarged prostate against the bladder.
U.S. Pat. No. 6,073,052 describes a method of sphincter treatment using a microwave antennae and specific time and temperature ranges, and U.S. Pat. No. 6,321,121 a method of GERD treatment using a non-specific energy source, with limited enabling specifications. The use of ultrasound energy for circumferential heating of the pulmonary vein to create electrical conduction block has been described in U.S. Pat. Nos. 6,012,457 and 6,024,740. The use of ultrasound for tumor treatments has been described in U.S. Pat. No. 5,620,479.
In view of the foregoing, and notwithstanding the various efforts exemplified in the prior art, there remains a need for a more simple, rapid, minimally invasive approach to treating sphincters that minimizes risk to the patient.